| Controlling the curing of a rubber compound -> Monitor Keywords |
|
|
 
Controlling the curing of a rubber compoundRelated Patent Categories: Data Processing: Generic Control Systems Or Specific Applications, Specific Application, Apparatus Or Process, Product Assembly Or Manufacturing, Particular Manufactured Product Or Operation, Molding, Control Of Curing, VulcanizationControlling the curing of a rubber compound description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070185611, Controlling the curing of a rubber compound. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This is a continuation application of a pending prior U.S. patent application Ser. No. 10/800,079, filed Mar. 11, 2004, which is a continuation-in-part application of prior U.S. patent application Ser. No. 10/666,433 filed Sep. 18, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/267,197 filed Oct. 8, 2002, now U.S. Pat. No. 6,855,791 issued on Feb. 15, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/394,736, filed Jul. 9, 2002. U.S. patent application Ser. No. 10/666,433 is also a continuation-in-part of both U.S. patent application Ser. No. 09/815,342, filed Mar. 21, 2001, and U.S. patent application Ser. No. 10/102,614, filed Mar. 19, 2002, now U.S. Pat. No. 6,774,643 issued on Aug. 10, 2004, which claims the benefit of U.S. Provisional Patent Application No. 60/278,034, filed Mar. 21, 2001; the entire disclosures of the above-cited prior applications are considered to be part of the present application accompanying application and accordingly are hereby fully incorporated by reference. RELATED FIELD OF THE INVENTION [0002] This invention relates to a new and improved process and apparatus for monitoring and controlling the vulcanization of natural and synthetic rubber compounds containing fillers such as carbon black, oils, clay, and the like. Typical base rubber polymers which may be employed include styrene-butadiene, polybutadiene, polyisoprene, ethylene-propylene, butyl, halobutyl, nitrile, polyacrylic, neoprene, hypalon, silicone, fluorcarbon elastomers, polyurethane elastomers, natural rubber and hydrogenated nitrile-butadiene rubber, and mixtures thereof. BACKGROUND OF THE INVENTION [0003] Heretofore methods of applying fixed process parameters to the processing of rubber polymeric compounds during vulcanization have resulted in both reduced productivity due to overly conservative cure times and poor product uniformity due to the inability of the fixed process parameters to accommodate the inherent variability in the process. [0004] The relationship of dielectric properties and the state and rate of the cure of polymers is well known. Related publications, incorporated herein fully by reference, in this field are: [0005] U.S. Patent Documents TABLE-US-00001 4,344,142 August 1982 Diehr, II et al. 4,373,092 February 1983 Zsolnay 4,399,100 August 1983 Zsolnay, et al. 4,423,371 December 1983 Senturia, et al. 4,496,697 January 1985 Zsolnay, et al. 4,510,103 April 1985 Yamaguchi, et al. 4,551,807 November 1985 Hinrichs, et al. 4,723,908 February 1988 Kranbuehl 4,777,431 October 1988 Day, et al. 4,773,021 September 1988 Harris, et al. 4,868,769 September 1989 Persson, et al. 5,032,525 July 1991 Lee, et al. 5,219,498 June 1993 Keller, et al. 5,317,252 May 1994 Kranbuehl 5,486,319 January 1996 Stone, et al. 5,528,155 June 1996 King, et al. 5,872,447 February 1999 Hager, III Other Publications [0006] Changes in the Electrical Properties of Natural Rubber/Carbon Black Compounds during Vulcanization, 1957, H. Desanges, French Rubber Institute [0007] A novel method of measuring cure--dielectric vulcametry, 1986, Sture Persson, The Plastics and Rubber Institute, England [0008] A comparative study of step curing and continuous curing methods, 1994, D. Khastgir, Indian Institute of Technology [0009] AC Impedance Spectroscopy of Carbon Black-Rubber composites, 1999, K. Rajeshwar, University of Texas at Arlington [0010] The prior art has clearly established a relationship between the dielectric (herein also referred to as "impedance") properties of polymeric resins and the curing of such resins. For example, these resins exhibit rheometric and chemical behavior such as melt, volatile release, gelation, and crosslinking that can be recognized by dielectric changes. However, unlike polymeric resins, rubber polymeric compounds do not melt or exhibit gelation during cure or vulcanization and are therefore much more difficult to characterize, monitor and control by analysis of dielectric characteristics. Moreover, none of the prior art associated with polymeric rubber curing (also referred to as "vulcanization") addresses the practical aspects of taking measurements directly in the production process, especially in the highly abrasive and high pressure environment of injection molding. Additionally the prior art does not show how to use the electrical data obtained to achieve closed-loop control of the curing or vulcanization process of, e.g., polymeric rubber over a wide range of molding methods and conditions. [0011] The prior art also does not show how to compensate, in the vulcanization process: (a) for variations in polymeric rubber curing compounds from batch to batch and within batches, and (b) for differences in vulcanizate thickness. Additionally, the prior art does not compensate for additional variables, which are introduced into the vulcanization process by the nature of the vulcanization equipment, tooling, and thermal history of polymeric rubber curing compounds. [0012] Moreover, the prior art uses dielectric or impedance measuring apparatus, which employ opposing and parallel electrodes of precise area and separation distance, and in which, the electrodes are in direct contact with the rubber compound. Although such electrodes and apparatus provide a means for measuring impedance properties during cure, they are entirely impractical for use in a production environment. For example, many rubber components are produced using injection molding technology which subjects the sensors to pressures up to 30,000 psi and temperatures up to 425.degree. F. Moreover, due to the flow inside the mold during injection, in addition to the carbon and silica fillers present in many rubber compounds, the sensor must survive in a highly abrasive environment. Finally, the sensor must also be able to survive mold cleaning via typical cleaning methods such as CO.sub.2 and plastic bead blast. [0013] Accordingly, it is desirable to have an apparatus and method for alleviating the above described drawbacks to using impedance data measurements for monitoring and controlling the vulcanization process for rubber polymeric compounds. In particular, it is desirable for the impedance sensor provided at the vulcanization equipment to be both extremely rugged and more easily used in that the electrodes: (a) need not be of precise area, (b) need not be of precise separation distance from one another, and (c) need not be in direct contact with the material being vulcanized. In addition, it would be desirable to have a method for correlating the desired properties of a rubber polymeric compound product with impedance measurements. DEFINITIONS AND TERMS [0014] Numerous technical terms and abbreviations are used in the description below. Accordingly, many of these terms and abbreviations are described in this section for convenience. Thus, if a term is unfamiliar to the reader, it is suggested that this section be consulted to obtain a description of the unknown term. [0015] Rubber Polymeric Compounds (equivalently, "Polymeric Rubber Compounds", and "Rubber Compounds" herein): Typical base rubber polymeric compounds including (but not limited to) styrene-butadiene, polybutadiene, polyisoprene, ethylene-propylene, butyl, halobutyl, nitrile, polyacrylic, neoprene, hypalon, silicone, fluorcarbon elastomers, polyurethane elastomers, natural rubber and hydrogenated nitrile-butadiene rubber (HNBR), and mixtures of such rubber compounds having fillers such as recited hereinabove. [0016] ODR: Oscillating Disk Rheometer--A device that measures the Theological characteristics (elastic torque, viscous torque, etc.) of a polymer during vulcanization, using an oscillating disk to apply stress to the curing polymer. [0017] MDR: Moving Die Rheometer--A device that measures the rheological characteristics (elastic torque, viscous torque, etc.) of a polymer during vulcanization, using a moving die to apply stress to the curing polymer. [0018] Rheometric instrument: A device that measures the rheological characteristics (elastic torque, viscous torque, etc.) of a polymer during vulcanization. [0019] T90 Time: The time, as measured in an ODR or MDR at which a given rubber compound at a given curing temperature, reaches 90% of its ultimate elastic torque value. Designed Experiment: A single set of related experiments drawn up from one of the types of designs to be found in the body of methods for design of experiments described hereinbelow in the Detailed Description. [0020] Exponential Dampening: The damping coefficient (.quadrature.) as defined by a best exponential fit to a set of raw data, where the fit curve (y) is described by the equation: y=Ae.sup.-.alpha.t, where t is time. [0021] Exponential Amplitude Coefficient: The amplitude coefficient (A) as defined by a best exponential fit to a set of raw data, where the fit curve (y) is described by the equation y=Ae.sup.-.alpha.t, where t is time. [0022] Topological Features of Impedance Related Data: Recognizable and distinct features within a cure curve, such as a peak (maxima), valley (minima) or flat (no slope). [0023] Low CTE Metallic Material: A material with a low coefficient of thermal expansion. [0024] Tool Steel: A steel suitable for use in making injection and compression molds such as AISI Type A2 Tool Steel. [0025] Witness cavity: A small cavity attached to but separate from injection mold for the rubber polymeric compound part being produced, wherein this small cavity is for allowing in-mold vulcanization sensor measurements of a rubber compound cure without the sensor being in direct contact with the curing part. In particular, a dielectric sensor in the witness cavity does not directly sense any of the parts that are being produced. Instead, the sensor monitors the cure of the rubber polymeric compound in the witness cavity. [0026] R-square (R.sup.2): R-square (also known as the coefficient of determination) is a statistical measure of the reduction in the total variation of the dependent variable due to the independent variables. An R-square close to 1.0 indicates that a model (also referred to herein as an "algorithm") accounts for almost all of the variability in the respective variables. [0027] Confidence interval: A range of values within which a particular number of interest is desired to be, at some specific level of probability such as 95%. SUMMARY OF THE INVENTION [0028] The present invention is a method and system for controlling the vulcanization (herein also denoted "curing") of rubber polymeric compounds. In particular, the present invention includes novel features for monitoring the polymerization and determining in real-time the optimum cure time for the production of parts made from rubber polymeric compounds (herein also denoted as "polymeric rubber compounds" or merely "rubber compounds" ). According to the present invention, during the curing of rubber polymeric compounds, data streams of impedance values are obtained (denoted herein as "impedance data streams"), wherein these values are indicative of impedance measurements obtained from one or more capacitor circuits (CC). Each of the capacitor circuits is operatively configured so that such a rubber polymeric compound becomes part of the capacitor circuit, and in particular, becomes a dielectric for the circuit. For each of the impedance data streams there is a corresponding graphical representation for presenting the particular impedance properties versus time that are provided by the impedance data stream. Such graphs are denoted "process curves" herein, and each such process curve is generally identical in informational content to the impedance data stream from which the process curve is derived. Accordingly, in many embodiments of the present invention utilizes derived characteristics of the impedance data streams that is more easily described in terms of their graphical representations as process curves, e.g., shape and/or geometric curve characteristics such as slopes and/or an area under such a process curve. Note that such impedance data streams can be representative of a time series of one or more of the following impedance types of impedance values: the impedance (Z), phase angle (o), resistance (R), reactance (X), conductance (G), and/or capacitance (C). Thus, the impedance data streams (and their related process graphs) are derived from the signal responses output by the activation of one or more of the capacitor circuits CC, wherein such activation is the result of at least one, and more generally, a plurality of signals of different frequencies being input to such capacitor circuit(s). Thus, in some embodiments of the present invention, each of the process curves may be obtained from a single, and in general different, signal frequency input to the capacitor circuit(s), and the corresponding shape (or other computational characteristics) of each of a process curves may be used in monitoring, controlling and/or predicting an outcome of a curing process for polymeric rubber compounds. [0029] In some embodiments of the present invention, various time series capacitor circuit output data components (i.e., impedance (Z), phase angle (o), resistance (R), reactance (X), conductance (G), or capacitance (C)) are separately processed, thereby resulting in a process curve with distinctive shape (or other features) for each of these components. Accordingly, it is an aspect of the present invention that such features from impedance (Z), phase angle (o), resistance (R), reactance (X), conductance (G), or capacitance (C) graphs (e.g., plotted versus time) can be used for monitoring and controlling the cure time by measuring a portion of the process curve and calculating or predicting the optimum cure time. Thus, since a particular shape (or other "computational features" such maxima, minima, slope, rate of slope, portion having substantially zero slope, inflection point, the area under a portion of the curve, etc.) of such process curves may be substantially repeatable for curing a particular rubber polymeric compound or material, such features can be effectively utilized in a mass production environment for producing consistent high quality cured products (e.g., seals, gaskets, and tires). [0030] Moreover, it is a further aspect of the present invention that for a given rubber polymeric material to be cured, the present invention can identify at least some of the computational features of these process curves substantially independently of the configuration of the product being produced by utilizing dielectric properties obtained from a "witness cavity" incorporated into the runner system (i.e., the flow path within the mold that channels the rubber to the product cavities) of the mold, as one skilled in the art will understand. In particular, such computational features can be correlated with the chemical and rheometric changes occurring during the curing process. [0031] Thus, although such process curves may vary in amplitude and duration (e.g., due to cured part thickness, thermal history, mold temperature and heat rate, curative level, compound batch variations, and various other factors), the present invention may be used for monitoring, controlling and/or predicting cure states of products in a mass production environment wherein the products being produced may be subject to significant process and rubber compound variation. [0032] For example, for a particular sample or product to be cured, properties of one or more of the above described process curves can be calculated for a specific measurement period wherein a portion of the data corresponding to each process curve of the sample may be correlated to a desired final cure state of the product. Thus, such a correlation can be used to establish a time for appropriately curing a part in production, wherein the part is substantially identical to the sample. In particular, the present invention predicts cure times as will be described more fully herein below. [0033] In one embodiment of the present invention, it has been found that during the curing of a polymeric rubber compound, there is a distinctive capacitance versus time process curve, and/or a distinctive conductance versus time process curve produced. Thus, for a part molded from a particular rubber polymeric compound, the shape of at least one of the corresponding distinctive capacitance and/or conductance process curves (for the particular rubber polymeric compound) may be consistent enough for predicting the state of the part during vulcanization. Thus, although such process curves for individual parts may vary in amplitude and time ordinates (principally due to part thickness, thermal history, mold temperature and heat rate, curative level, and various other factors), the general shape of such curves can be used in predicting the state of vulcanization. That is, the shape of such process curves can be correlated to the chemical and physical changes occurring during the curing process. [0034] For example, the initial slope of at least one of the distinctive capacitance and conductance process curves for a rubber compound being cured is associated with the rate of the curing reaction and this initial slope can be used to establish or predict the preferred or correct cure time for the polymeric rubber part being produced. In addition, the area under such a process curve or a portion of the process curve may be associated with the cure "energy" and can be also be used to control or predict the cure time. For certain rubber compounds, one or more of the capacitance and conductance process curves exhibit a shape including a "VALLEY" and/or a "PEAK" which can be used to control or predict the cure time. Moreover, it is an aspect of the present invention to employ software algorithms for identifying process curve features, wherein such algorithms compute process curve characteristics such as linear fit coefficients, polynomial fit coefficients, and logarithmic fit coefficients so that these computed characteristics can be used to control the cure time and thereby achieve a desired part property such as a predetermined range of tensile strength and/or compression set. Continue reading about Controlling the curing of a rubber compound... Full patent description for Controlling the curing of a rubber compound Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Controlling the curing of a rubber compound patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Controlling the curing of a rubber compound or other areas of interest. ### Previous Patent Application: Robot system and method for the application of dislodging material and pin positioning in casting wheels Next Patent Application: Systems and methods for managing inventory of aggregated post-consumer goods Industry Class: Data processing: generic control systems or specific applications ### FreshPatents.com Support Thank you for viewing the Controlling the curing of a rubber compound patent info. IP-related news and info Results in 0.14987 seconds Other interesting Feshpatents.com categories: Tyco , Unilever , Warner-lambert , 3m 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
